The generation and characterization of human monoclonal antibodies, in contrast to murine systems, has been difficult and with few exceptions, non-productive. In fact, current hypotheses of Ig gene usage in human organ specific autoimmune diseases are either extrapolated from murine lupus or based on analysis of rheumatoid factors. My laboratory has been successful in generating combinatorial autoantibodies derived from the lymph node of patients with primary biliary cirrhosis (PBC). These Fab autoantibodies are directed at PDC-E2, the major autoantigen of PBC. Moreover, the nucleotide sequence of our combinatorial autoantibodies suggest that these antibodies are clonally related and reflect a restricted response to PDC-E2. Moreover, the V-H genes show considerable somatic mutation in CDR and three of these antibodies utilize a V-H germline gene that has not hitherto been published. PBC is one of the few autoimmune diseases for which a) the autoantigen and dominant epitope have been identified; b) the genes coding for these autoantigens have been cloned and sequenced; and c) recombinant proteins and synthetic peptides are available. In this First Award I will take advantage of these strengths and address several key questions. For example, we will obtain additional data on the Ig gene usage encoding autoantibodies to PDC-E2 and BCKD-E2: more than 90% of patients with PBC react with one or more of these autoantigens. We will also determine, as our pilot data suggests, that these autoantibodies are encoded by a restricted response, reflect uncommon gene usage, and have undergone somatic mutation. Additionally, we will determine similarities which exist between the coding sequences of autoantibodies to PDC-E2 compared to BCKD-E2. Finally, we will take advantage of our random peptide library (peptide on plasmid) and determine the autoepitopes recognized by these autoantibodies. We will compare such data to epitopes determined by overlapping recombinant peptides. Such data is important because by confocal microscopy we have demonstrated that our combinatorial autoantibodies stain a unique protein located only on the luminal side of bile duct epithelial cells in patients with PBC but not PSC. Further data on epitope recognition and mapping may shed further light on this issue. The answers to these issues will have significant implications not only for PBC, but also for other organ specific autoimmune diseases and will provide significant data on the utility of combinatorial autoantibodies.